A. Field of the Invention
The invention relates to electrolytic cells for electrochemical synthesis.
B. Description of the Prior Art
Electrochemical devices employing stacked plates are well-known in the art. Conventional stacked plate cells include arrangements wherein planar electrodes of circular shape are located in an electrolyte chamber, spaced apart with radial insulating strips in the form of a stack, in which, with the exception of the outermost electrodes, each electrode acts both as anode and cathode. The electrolyte liquid is fed into the center of the stack, so that, it is operably exposed to the electrodes as it passes outwardly to the periphery of the electrodes. The spacing of the electrodes is fixed by radial strips of insulating non-swelling materials of the desired thickness.
The spacing of the bipolar electrode plates can vary within wide limits, but should be from 0.5 mm to 2 mm. This is because for many electrochemical reactions it is desirable to select a very small spacing so as to keep down the cell voltage and hence the power consumption, and to achieve a high space-time yield, and a low volume flow rate of the circulating electrolyte at a given flow rate.
The prior art teaches that the plates themselves can be circular or be of approximately circular geometrical shape; and that a circular shape permits industrial manufacture of plates of high quality without great expense and makes it possible to set the electrode spacing to less than 1 mm.
With this type of cell construction, the liquid which externally surrounds the plate stack in operation is an electrical shunt, but this is a relatively unimportant factor in electrochemical synthesis if the plate thickness is large compared to the thickness of the capillary gap and can be made even less important if the electrode plates are each surrounded by tightly fitting rings of insulating material. Such a cell construction is taught in U.S. Pat. No. 4,048,047, in which a center feed was employed.
One of the major disadvantages of the stacked cell assembly with center feed, is that the electrode exposure to the electrolyte is not uniform in the sense that there is a greater electrolyte velocity along the inner portions of the electrodes than along the peripheral portions. This inevitably results in a dissimilar exposure pattern between the inner surfaces and the outer surfaces of the electrode. Wherever velocity affects product selectivity, of course, such variations in velocity may substantially affect overall selectivity or yield. In the cell with center feed, moreover, current leakage from within the center feed portion by way of an electrical shunt may be significant.
Since the stacked electrochemical cell is of increasing interest commercially, an electrode arrangement which eliminates the above described disadvantages would represent a significant contribution and advancement in the art, and is an object of this invention.
More specific objects of this invention are specified below.